Signal Power MCQ Quiz - Objective Question with Answer for Signal Power - Download Free PDF
Last updated on Jun 26, 2025
Latest Signal Power MCQ Objective Questions
Signal Power Question 1:
An impedance of an antenna is 40 Ω. An unmodulated AM signal produces a current of 5 A. Assuming total power of 1295 W, determine the sideband power:
Answer (Detailed Solution Below)
Signal Power Question 1 Detailed Solution
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Explanation:
Given Problem:
An antenna has an impedance of 40 Ω. An unmodulated AM signal produces a current of 5 A. The total power of the AM signal is given as 1295 W. The task is to determine the sideband power (PSB).
Solution:
In amplitude modulation (AM), the total power (PT) is the sum of the carrier power (PC) and the sideband power (PSB). Mathematically, this can be expressed as:
PT = PC + PSB
Where:
- PT = Total power
- PC = Carrier power
- PSB = Sideband power
To solve the problem, let us calculate the carrier power first.
Step 1: Calculate the Carrier Power (PC)
The carrier power is given by the formula:
PC = I² × R
Where:
- I = Carrier current (in amperes)
- R = Impedance of the antenna (in ohms)
Substitute the given values:
PC = 5² × 40
PC = 25 × 40
PC = 1000 W
Thus, the carrier power is 1000 W.
Step 2: Calculate the Sideband Power (PSB)
The total power (PT) is provided as 1295 W. From the total power formula, we know:
PT = PC + PSB
Rearranging for PSB:
PSB = PT - PC
Substitute the known values:
PSB = 1295 - 1000
PSB = 295 W
Thus, the sideband power is 295 W.
Final Answer:
The sideband power is 295 W, which corresponds to Option 4.
Additional Information
To further analyze the correctness of the other options, let's review them based on the solution:
Option 1 (800 W):
This option is incorrect. The sideband power (PSB) is calculated as 295 W, not 800 W. The value of 800 W is far too high and does not match the given total power or the calculated carrier power.
Option 2 (2800 W):
This option is also incorrect. A sideband power of 2800 W exceeds the given total power (1295 W), which is not feasible. Such a value is physically inconsistent with the problem's parameters.
Option 3 (2295 W):
This option is incorrect as well. A sideband power of 2295 W is unrealistic and does not align with the calculated values. The total power is only 1295 W, so the sideband power cannot exceed this value.
Option 4 (295 W):
This is the correct option. As derived above, the sideband power is 295 W, which matches the calculations based on the given data.
Option 5 (No value provided):
This option is invalid as it does not provide any numerical value for the sideband power.
Conclusion:
In amplitude modulation, the total power is the sum of the carrier power and the sideband power. Using the given data, the carrier power was calculated as 1000 W, and the sideband power was determined to be 295 W. Therefore, the correct answer is Option 4.
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Signal Power Question 2:
The antenna current of an AM transmitter is 6 A (unmodulated). Determine the antenna current of the transmitter when the percent of modulation changes to 0.4.
Answer (Detailed Solution Below)
Signal Power Question 2 Detailed Solution
Concept:
The total transmitted power for an AM system is given by:
Pt = It2 R (Transmitted Power)
PC = Ic2 R (Carrier Power)
It = RMS value of antenna current before modulation
Ic = RMS value of antenna current after modulation
R = Antenna Resistance
∴ The antenna current of modulated and un-modulated carrier signal is related as:
Calculation:
Given IC = 6 A. Modulation index = 0.4.
It = 6√1.08 = 6 × 1.039
It = 6.23 A
Signal Power Question 3:
Calculate the power of the transmitted wave in an amplitude modulated system if the power of the carrier is 100 W and the depth of modulation is 80%
Answer (Detailed Solution Below)
Signal Power Question 3 Detailed Solution
Concept:
The total transmitted power for an AM system is given by:
Pc = Carrier Power
μ = Modulation Index
Calculation:
Given μ = 80% = 0.8
Pc = 100 W
Pt = 132 W
Signal Power Question 4:
In an AM system, the modulating signal is a sinusoid with frequency of fm Hz. If 80% modulation is used, then the ratio of total side-band power in the modulated signal, to the total power is:
Answer (Detailed Solution Below)
Signal Power Question 4 Detailed Solution
Concept:
Total power is given by:
The required ratio of sideband power to total power will be:
Calculation:
Given, m = 0.8
Signal Power Question 5:
The unmodulated carrier power in an AM transmitter is 5 kW. This carrier is modulated by a sinusoidal modulating signal. The maximum percentage of modulation is 50%. If it is reduced to 40%, then the maximum unmodulated carrier power (in kW) that can be used without overloading the transmitter is _________
Answer (Detailed Solution Below) 5.19 - 5.23
Signal Power Question 5 Detailed Solution
Concept: Total power of AM transmitter is given by
Application: Given, Pc = 5 kW (Carrier Power)
μ = 0.5
= 5k (1 + 0.125)
Pt = 5k × 1.125
μ is now reduced to μ = 0.4
If the transmitter is not to be overloaded i.e. if Pt is to remain the same,
The maximum unmodulated carrier power which can be used is,
⇒ 5.2 KW
Top Signal Power MCQ Objective Questions
Consider the following amplitude modulated signal: s(𝑡) = cos(2000 𝜋𝑡) + 4 cos(2400 𝜋𝑡) + cos(2800 𝜋𝑡).The ratio (accurate to three decimal places) of the power of the message signal to the power of the carrier signal is ________.
Answer (Detailed Solution Below) 0.125
Signal Power Question 6 Detailed Solution
Download Solution PDFConcept:
For a single-tone sinusoidal signal, the expression for amplitude modulated wave is given by:
Calculation:
Comparing the given expression with the standard expression, the given AM signal can be written as:
For a sinusoidal signal ratio of sideband power to carrier power is given:
=
=
=
= 0.125
Special Note: It is an Official GATE Question. The question was challenged to GATE regarding the answer key. If we consider the sideband power as the message signal power, we'll get 0.125 as the ratio, but if we solve it by comparing the given expression with the standard expression, we'll 0.25 as explained in the solution.
The antenna current of an AM transmitter is 6 A (unmodulated). Determine the antenna current of the transmitter when the percent of modulation changes to 0.4.
Answer (Detailed Solution Below)
Signal Power Question 7 Detailed Solution
Download Solution PDFConcept:
The total transmitted power for an AM system is given by:
Pt = It2 R (Transmitted Power)
PC = Ic2 R (Carrier Power)
It = RMS value of antenna current before modulation
Ic = RMS value of antenna current after modulation
R = Antenna Resistance
∴ The antenna current of modulated and un-modulated carrier signal is related as:
Calculation:
Given IC = 6 A. Modulation index = 0.4.
It = 6√1.08 = 6 × 1.039
It = 6.23 A
The unmodulated carrier power in an AM transmitter is 5 kW. This carrier is modulated by a sinusoidal modulating signal. The maximum percentage of modulation is 50%. If it is reduced to 40%, then the maximum unmodulated carrier power (in kW) that can be used without overloading the transmitter is _________
Answer (Detailed Solution Below) 5.19 - 5.23
Signal Power Question 8 Detailed Solution
Download Solution PDFConcept: Total power of AM transmitter is given by
Application: Given, Pc = 5 kW (Carrier Power)
μ = 0.5
= 5k (1 + 0.125)
Pt = 5k × 1.125
μ is now reduced to μ = 0.4
If the transmitter is not to be overloaded i.e. if Pt is to remain the same,
The maximum unmodulated carrier power which can be used is,
⇒ 5.2 KW
An impedance of an antenna is 40 Ω. An unmodulated AM signal produces a current of 5 A. Assuming total power of 1295 W, determine the sideband power:
Answer (Detailed Solution Below)
Signal Power Question 9 Detailed Solution
Download Solution PDF```html
Explanation:
Given Problem:
An antenna has an impedance of 40 Ω. An unmodulated AM signal produces a current of 5 A. The total power of the AM signal is given as 1295 W. The task is to determine the sideband power (PSB).
Solution:
In amplitude modulation (AM), the total power (PT) is the sum of the carrier power (PC) and the sideband power (PSB). Mathematically, this can be expressed as:
PT = PC + PSB
Where:
- PT = Total power
- PC = Carrier power
- PSB = Sideband power
To solve the problem, let us calculate the carrier power first.
Step 1: Calculate the Carrier Power (PC)
The carrier power is given by the formula:
PC = I² × R
Where:
- I = Carrier current (in amperes)
- R = Impedance of the antenna (in ohms)
Substitute the given values:
PC = 5² × 40
PC = 25 × 40
PC = 1000 W
Thus, the carrier power is 1000 W.
Step 2: Calculate the Sideband Power (PSB)
The total power (PT) is provided as 1295 W. From the total power formula, we know:
PT = PC + PSB
Rearranging for PSB:
PSB = PT - PC
Substitute the known values:
PSB = 1295 - 1000
PSB = 295 W
Thus, the sideband power is 295 W.
Final Answer:
The sideband power is 295 W, which corresponds to Option 4.
Additional Information
To further analyze the correctness of the other options, let's review them based on the solution:
Option 1 (800 W):
This option is incorrect. The sideband power (PSB) is calculated as 295 W, not 800 W. The value of 800 W is far too high and does not match the given total power or the calculated carrier power.
Option 2 (2800 W):
This option is also incorrect. A sideband power of 2800 W exceeds the given total power (1295 W), which is not feasible. Such a value is physically inconsistent with the problem's parameters.
Option 3 (2295 W):
This option is incorrect as well. A sideband power of 2295 W is unrealistic and does not align with the calculated values. The total power is only 1295 W, so the sideband power cannot exceed this value.
Option 4 (295 W):
This is the correct option. As derived above, the sideband power is 295 W, which matches the calculations based on the given data.
Option 5 (No value provided):
This option is invalid as it does not provide any numerical value for the sideband power.
Conclusion:
In amplitude modulation, the total power is the sum of the carrier power and the sideband power. Using the given data, the carrier power was calculated as 1000 W, and the sideband power was determined to be 295 W. Therefore, the correct answer is Option 4.
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Signal Power Question 10:
Calculate the power of the transmitted wave in an amplitude modulated system if the power of the carrier is 100 W and the depth of modulation is 80%
Answer (Detailed Solution Below)
Signal Power Question 10 Detailed Solution
Concept:
The total transmitted power for an AM system is given by:
Pc = Carrier Power
μ = Modulation Index
Calculation:
Given μ = 80% = 0.8
Pc = 100 W
Pt = 132 W
Signal Power Question 11:
Consider the following amplitude modulated signal: s(𝑡) = cos(2000 𝜋𝑡) + 4 cos(2400 𝜋𝑡) + cos(2800 𝜋𝑡).The ratio (accurate to three decimal places) of the power of the message signal to the power of the carrier signal is ________.
Answer (Detailed Solution Below) 0.125
Signal Power Question 11 Detailed Solution
Concept:
For a single-tone sinusoidal signal, the expression for amplitude modulated wave is given by:
Calculation:
Comparing the given expression with the standard expression, the given AM signal can be written as:
For a sinusoidal signal ratio of sideband power to carrier power is given:
=
=
=
= 0.125
Special Note: It is an Official GATE Question. The question was challenged to GATE regarding the answer key. If we consider the sideband power as the message signal power, we'll get 0.125 as the ratio, but if we solve it by comparing the given expression with the standard expression, we'll 0.25 as explained in the solution.
Signal Power Question 12:
If the modulation index of an AM wave is changed from 0 to 1, the transmitted power
Answer (Detailed Solution Below)
Signal Power Question 12 Detailed Solution
Concept:
The total transmitted power for an AM system is given by:
Pc = Carrier Power
μ = Modulation Index
Analysis:
When μ = 0, the transmitted power will be:
When μ = 1, the transmitted power will be:
The % increase in the modulated signal power is given by:
Signal Power Question 13:
The antenna current of an AM transmitter is 6 A (unmodulated). Determine the antenna current of the transmitter when the percent of modulation changes to 0.4.
Answer (Detailed Solution Below)
Signal Power Question 13 Detailed Solution
Concept:
The total transmitted power for an AM system is given by:
Pt = It2 R (Transmitted Power)
PC = Ic2 R (Carrier Power)
It = RMS value of antenna current before modulation
Ic = RMS value of antenna current after modulation
R = Antenna Resistance
∴ The antenna current of modulated and un-modulated carrier signal is related as:
Calculation:
Given IC = 6 A. Modulation index = 0.4.
It = 6√1.08 = 6 × 1.039
It = 6.23 A
Signal Power Question 14:
When modulation percentage is 75%, an AM transmitter produces 10 kW of power. The percentage of power saving If the carrier and one of its side bands are suppressed before transmission is ________ %.
[Upto 2 decimal places]
Answer (Detailed Solution Below) 88.95 - 89.06
Signal Power Question 14 Detailed Solution
Concept:
Power of full
Power in carrier = Pc
Power in 2 side bands
Power in 1 sideband
Calculation:
When carrier and 1 side band is suppressed,
Percentage power saved:
u = 0.75
Signal Power Question 15:
An AM broadcast station transmits an average carrier power output of 40 kW and used a modulation index of 0.65 for sine wave modulation. What is the maximum peak amplitude of output if effective impedance of antenna is 50 Ω ________ (in kV)
Answer (Detailed Solution Below) 3.2 - 3.4
Signal Power Question 15 Detailed Solution
Given carrier power Pc = 40 kW
Modulation index ma = 0.65
Since
⇒ Ac = 2 × 103V
Message amplitude Am = 0.65 × 2 × 103
= 1300 V
Peak value of Am wave = Am + Ac
= 2000 + 1300
= 3.3 kV